Ribose-5-Phosphate Isomerase Deficiency
What else is it called?
- RPI Deficiency
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What causes it?
This disorder is caused by a problem in the RPI(Ala61Val) allele. This allele provides instructions for enzymes that are part of the Pentose Phosphate Pathway. This process is needed for the generation of NADPH.
If you have a problem in the RPI(Ala61Val) allele, you will not have enough of the enzyme needed for the conversion of ribulose-5-phosphate into ribose-5-phosphate. This causes a build-up of the molecules ribitol and D-arabitol within the body.
How common is it?
There has been only one reported case of Ribose-5-Phosphate deficiency in medical history. Because of this there is no known knowledge about the disease’s carrier frequency or universal prevalence.
What are the signs and symptoms?
The known signs and symptoms develop from early childhood and can be progressive. They include:
- Neurological regression
- Abnormalities of the cerebral white matter region
There is no known life expectancy for the disease.
How is it diagnosed?
The main method of diagnosis for Ribose-5-Phosphate Isomerase deficiency is through measurement of ribitol and D-arabitol levels within the brain and bodily fluids. Elevated levels indicate that there is a defect in the RPI(Ala61Val) allele. Decreased levels of certain molecules in the urine can be used to support a diagnosis.
Ribose-5-Phosphate Isomerase deficiency is not tested for in any newborn screening tests.
Can it be treated?
Unfortunately, there is no known treatment or prognosis for patients diagnosed with this disease.
Do my family need to be tested?
RPI is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of RPI is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with RPI are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.